February 2, 2023


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View in space: The world’s largest radio telescope under construction

Status: 12/17/2022 8:57 AM

The huge radio telescope called the Square Kilometer Array should help learn more about the universe and its composition. What makes this radio telescope so special?

Written by Uwe Gradwohl and Ralf Kölbel, SWR

It looks like several huge fields of shiny Christmas trees in the middle of the red outback of Australia – at least once you’re done. This is just one of two parts Square kilometer radio telescope arrayOr, for short: SKA. It is considered one of the greatest research tools and most ambitious scientific projects of the 21st century. The telescope is called a “square kilometer” because its more than 130,000 antennas will provide a reception area of ​​half a square kilometer after its completion. Construction began in early December 2022 after decades of diplomatic negotiations over financing.

on two continents

When fully expanded, a telescope with 131,072 two-meter-high fir-tree-like antennas in Australia and an additional 130 parabolic antennas, each 15 meters in diameter, in South Africa will be able to decipher the mysteries of our universe.

The antenna’s range extends over great distances. In Australia, smaller wire antennas are distributed over 65 km, and parabolic mirrors in South Africa over 150 km. The two antenna fields scan the sky in different frequency bands and look in different directions during regular operation. But if something special happens in space, the two telescope fields can pair up with each other and at the same time catch a glimpse of the same object.

Radio telescopes also search for light

Visible light makes up only a small part of the electromagnetic spectrum. Above visible light, that is, at high vibration frequencies of electromagnetic waves, the ultraviolet regions begin, as well as X-rays and gamma rays. The infrared range of the electromagnetic spectrum begins below visible light, that is, at a lower frequency. For example, the James Webb Space Telescope operates in the infrared. Even the lower frequencies of the waves are referred to as radio emissions.

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So a radio telescope also looks at light, but light at a frequency that is not visible. It is a kind of technical “eye” for radio emissions. Bonn astrophysicist Michael Kramer said in an interview with The SWR“,” Then the universe will look very different to us.

A deep look into the past of the universe

The researchers want to use the new radio telescope to find out how the first stars and galaxies formed. “To this day we don’t know: what is dark energy? What is dark matter?” says Michael Kramer, an astrophysicist at the Max Planck Institute for Radio Astronomy in Bonn.. “Are the laws of gravity in Albert Einstein’s theory of relativity correct or not? These are all questions we cannot answer yet. A telescope will be very useful in getting us at least one step closer to the answer.”

According to Kramer, the universe was initially very hot after the Big Bang, but then cooled down, but remained starless. And only then did gravity begin to “clump” the omnipresent hydrogen. This is how the first stars were formed. With their radiation, they ionized the hydrogen in their environment, i.e. electrons were “snatched” from the hydrogen atoms.

Information about the formation of galaxies

Astrophysicists want to use the SKA Space Telescope to receive and examine the weak, extremely low-frequency radio signals that are being generated. This aims to give a better understanding of how the first galaxies, stars and black holes formed after the Big Bang from ordinary hydrogen as the starting material.

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“There is no other way to actually make these waves visible,” says Kramer, or to measure them and look for the signal to see how the universe is evolving. There are many things that can only be observed in the radio band. For example, radio pulsars or the light from black holes.”

Up to a hundred times more sensitive than previous telescopes

According to astrophysicist Kramer, the telescope will be up to a hundred times more sensitive in the final stage than the radio telescopes currently available to researchers. In particular, SKA can also capture radio emissions from the early days of the universe. Radio waves, which have been traveling through space for billions of years, are gradually decreasing in frequency as the universe expands. If you want to look far into the past, according to Kramer, you have to do so in lower frequencies. This is what antennas are for.

In the most remote places in the world

The areas where the antennas are installed are some of the most remote in the world. Because this sensitive telescope also picks up many signals that interfere with the search, such as mobile phone signals and radio stations. “If you were to put a cell phone on the Moon, even as far as the Earth and the Moon are, the cell phone would be the third most powerful radio source in the sky,” Kramer said.

However, the sources the researchers want to look at, such as signals from the early universe, are up to a billion times weaker. In order to avoid interference, telescopes are built in areas with little civilization. Both locations, in Australia and South Africa, are in so-called “radio silent zones”. They are prohibited by law from setting up radio stations.

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German research policy is far from legitimate

Germany was a founding member of the SKA Federation in 2011. In 2015 the federal government withdrew from the project for financial reasons. This was generally unfortunate in the radio astronomy community – especially since Germany had played a leading role in an important earlier project in South Africa. Since 2019 Max Planck Society Interests of German researchers in the circle of SKA countries. Not a perfect solution, but this way German radio astronomers can contribute more and make full use of the data.

Astrophysicist Kramer expects the first antennas to be operational in 2027. The SKA is also a private telescope you can work with while it’s still under construction: “I’m really looking forward to seeing this data.”